Measurement of flanking transmission in outer walls in test facilities

Applied Acoustics 40 (1993) 239-254

Measurement of Ranking Transmission in Outer Walls in Test Facilities J. L a n g Versuchsanstalt ftir W/trine und Schalltechnikam TGM Wien, A-1200 Wien, Wexstrasse 19-23, Austria

ABSTRACT In Austrian residential buildings flanking sound transmission in outer walls ---designed to ensure good heat insulation--influences the sound insulation between horizontally and vertically adjacent dwellings considerably due to different resonance effects. To carry out research on measures to increase flanking sound insulation and to give data on which calculations on sound insulation can be based, a test facility was constructed where horizontal and vertical flanking sound transmission in outer walls connected to different types of partitions and floors can be measured The construction of the test facilities is described in detail and results of measurements on different types of typical Austrian outer walls are reported The measurement results are compared with calculations based on the new Austrian standard.

INTRODUCTION Measurements in residential buildings have shown that in most cases sound insulation between adjacent rooms is determined by the flanking elements as well as by the partition. This is especially true between rooms separated by a concrete plate with floating floor (the usual construction in Austria), where the outer walls and lightweight walls flanking the floor determine the sound insulation. 1,2 It is found that the outer walls commonly used in Austria, which have been designed to ensure very good heat insulation, lack sound insulation and this also influences flanking sound transmission. In Austria about 60% of dwellings are constructed with outer walls from hollow bricks, 15% with hollow concrete blocks, 8% with jacket blocks from woodchips 239 Applied Acoustics 0003-682X/93/$06.00 © 1993 Elsevier Science Publishers Ltd, England.

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concrete. All of these types are also layered with styrofoam or mineral wool. These walls have much lower sound insulation than whould be expected from their mass. This is caused by resonance. Figure l(c) shows measured values of sound reduction index versus frequency for some of these walls. Figure l(a) and (b) shows the weighted sound reduction index versus mass per unit area, all measured

Flanking transmission in outer walls

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in the laboratory without flanking transmission. With respect to these results it is of great interest to the Austrian building industry to get detailed information on sound insulation of the different pi'oducts and on the flanking sound transmission in outer walls of the different types of products. The latter was of special interest with respect to the fact that the Austrian standard O N O R M B 8115, part 43 was prepared with a prediction scheme for sound insulation in buildings, based on the weighted sound reduction index Rw of partition and flanking elements and on the junction level difference Dv, as given below. The standardized sound level difference between two rooms is calculated from (all calculations are done with single numbers):

Dn,~,w = - 1 0 lg 10DR'T'w'~I0+~ 1 0 -DR'T''f'jI° i= 1

where Dn,x,w = weighted standardized sound level difference in dB; Dn,~,w,d = weighted standardized sound level difference given by the partition in dB; Dn,r,wS,i = weighted standardized sound level difference given by the ith flanking element in dB; and n = number of flanking elements. D~,r,w,d = R,,,d - 1 0 lg Sd + 10 lg V - 5 Dn,T,w,f, i "- - - 1 0 lg (10 -°".T.'.Ff,'/l° + 10 -°",T,W'~,'/l° + 10 -°",r.''",'/l°) D,,T,w,Ff,; = Rw,f,i + Dv,rf,~ - 1 0 lg Sr,~ + 10 lg V - 5 Dn,T,w,Df,~= Rw,d + Dr,Dr,; --10 lg Sf,~+ 10 lg V - 5 Dn,T,w,Vd,i= Rw,f,i + Dv,vd,i --10 lg Sd + 10 lg V - 5 where Rw,d = weighted sound reduction index of the partition in dB; Rw,f,; = weighted sound reduction index of the ith flanking element in dB; Sd - area of the partition in m:; Sf,~ = area of the ith flanking element in the receiving room in m2; V = volume of the receiving room in m3; and Dv,r:f,~, Dv,Df,;, Dv,Fd,~-- level difference at the junction for the ith flanking element in dB for the paths Ff, Df, Fd. It was to be determined which values for Rw and D~ should be inserted into the calculation for the above mentioned special types of outer walls.

TEST FACILITIES In 1987/1988 a test facility was constructed at our institute in connection with the existing laboratory with the support of the Fachverband der Stein- und keramischen Industrie Osterreichs subsidized by the Bundesministerium ftir wirtschaftliche Angelegenheiten, Wohnbauforschung, and the Forschungsf6rderungsfonds der gewerblichen Wirtschaft Osterreichs. The facilities consist of five rooms and make it possible to measure

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Hg. 3. Partition between rooms 1 and 2 and lloor in these rooms. flanking sound transmission in horizontal and vertical directions. This seemed necessary with respect to the different types of joints in walls of hollow bricks and concrete blocks and the different types of junctions in outer walls with partitions and with floors. In Fig. 2 the ground plan and section are shown. Within the four rooms in the basement and the one room in the upper floor the following measurements can be carded out, when a test wall of about 30 m 2 has been inserted: -

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MEASUREMENTS The aim of the investigation was primarily to measure flanking sound transmission in the different types of outer walls. For these measurements the outer wall was installed (see Fig. 8) connecting rooms i, 2 and 5 and the junction to the partition or floor constructed in different ways with

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lightweight (gypsum board) walls or floors, heavy concrete walls or floors or with a wall usually used together with the outer wall (e.g. with an outer wall of jacket blocks usually a partition wall of jacket blocks is used). To characterize the flanking sound transmission the flanking-normalized sound level difference D.,L was measured and also the single number Dn,L,w calculated. The value of D.,L,w can also be inserted into the calculation of D.,T,. in buildings via the sound path Ff with Dn,T,wFf = D.,L,w - 10 lgi0Sn2 + 10 lg30r~V~3 where S = area of the flanking wall in the receiving room in the building in m2; and V -- volume of the receiving room in the building in m 3. For the different types of junctions the level difference D. was also measured; measurements were carried out using excitation with airborne sound and with structure-borne sound with a vibration exciter.

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Fig. 7. Sound insulation between test rooms for vertical transmission without flankiilg wall. The level decrease within a wall, e.g. caused by a special type of joints between the bricks, can be measured with velocity level difference in the wall in different distances from the junction in the receiving room: these measurements also can be done with airborne or structure-borne sound excitation. The results from measurements carried out with both types of excitation showed good agreement. M E A S U R E M E N T R E S U L T S F O R SPECIAL TYPES OF OUTER WALLS Hollow bricks

Measurements were carried out with two types of hollow bricks with two different types of junctions. The results for a 38-cm wall are shown in

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Fig. 9. The sound reduction index shows the resonance above 800 Hz; this resonance also influences the flanking transmission. Sufficient sound insulation can only be achieved with a partition of heavy concrete which separates the two outer walls totally (theoretical example only which cannot be introduced into building practice). Measurements with the concrete wall inserted into the outer wall to different depths showed that the greater the depth of the separating concrete wall in the outer wall, the higher the flanking sound insulation. In Fig. 10 the measured values of Dv are shown. In Table 1 the values of Dr, measured and calculated according to the mass ratio are compared. It can be seen that the calculated value is achieved with the TABLE 1

Calculated and Measured Values of Dv Partition

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Fig. 9. S o u n d reduction index and h o r i z o n t a l and vertical f l a n k i n g - n o r m a l i z e d level difference o f a wall from 38-cm h o l l o w bricks, plaster on both sides, 420 (---) S o u n d reduction index (average) R,~ = 53 dB; ( . . . . ) j u n c t i o n g y p s u m board = 57 dB; ( . . . . . . ) j u n c t i o n concrete separating brick wall Dn,L, w = 66 dB; ( tion concrete floor 27 cm, fixed into brick wall D . . L ~ - 61 dB.

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concrete wall separating the outer wall; however, is not achieved with the floor only inserted 27 cm into the 38-cm outer wall. From measurements of the velocity level in the outer wall in the receiving room at two different distances from the junction, a level decrease within the wall can be found. This could be caused by a special type of mortar joint. In Fig. 11 the velocity level difference in 2-1 m horizontal distance and in 1.3 m vertical distance is drawn. It can be seen that the special type of vertical joint with mortar only in two hollows gives a level difference in the high-frequency range, whereas the horizontal joint with a continuous layer of mortar does not. 20

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From measurements of the velocity level and the airborne sound pressure level in the receiving room the sound radiation efficiency can also be determined for direct airborne sound excitation and for excitation via the junction. The results are shown in Fig. 12 for two-hollow brick walls. Jacket blocks from woodchip concrete Outer walls from jacket blocks filled with concrete are acoustically multilayer systems, especially the types with layers of polystyrol in the outer ~0

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Fig. 13. Outer wall and partition from jacket blocks from woodchip concrete part of the block. D u e to resonance, the sound insulation of walls ~ lower than expected from their mass. However, due to the fact that the resonance system is in the outer part of the wall it can be expected that it does not influence the flanking sound insulation. Measurements were therefore carried out with a system as shown in Fig. 13. The results showed that the resonance influences the sound reduction index, but does not influence the flanking sound insulation. F r o m this result it turns out that the flanking sound insulation cannot be calculated from the sound reduction index plus junction level difference but has to be measured.

Hollow concrete blocks with insulating layers Some types of hollow concrete blocks are designed with layers of styrofoam to ensure good heat insulation; due to the resonance system (mass-

Flanking transmission in outer walls

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spring) the sound reduction index shows a dip in the main frequency range. Measurements were carried out with an outer wall of 38-cm blocks of Leca-concrete with 6.6-cm polystyrol layer (with no concrete bridge between the two concrete leaves). Figure 14 shows the outer wall and the partition. Figure 15 shows the results for the sound reduction index and the flanking-normalized sound level difference; additional measurements were carried out with the 20-cm inner concrete block leaf alone, with plaster on both surfaces. It can be seen that the resonance reduces the sound reduction index as well as the flanking sound insulation. Figure 16 shows the difference in sound insulation for R and for Dn,r for the total block and for the inner leaf. The example shows that for this type of outer walls the sound reduction index of the whole wall plus junction level difference calculated via mass-ratio determines the flanking sound insulation.

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Fig. 15. Sound reduction index and horizontal and vertical flanking-normalized sound level difference of outer wall from hollow concrete blocks with layer of polystyrene (410 kg/m2). ( ) Sound reduction index (average) Rw = 50 dB; ( - - - ) horizontal flanking-normalized sound level difference D,.L, w = 60 dB; (. . . . ) vertical flanking-normalized sound level difference Dn.L.w -- 64 dB; for comparison: 20 cm inner leaf of the wall, plaster on both sides, 354 kg/m2; ( ) sound reduction index (average) Rw = 52 dB; (- -) horizontal flanking-normalized sound level difference Dn,Lw ---- 59 dB; (..... ) vertical flanking-normalized sound level difference d,,L,,~ -- 67 dB.

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Fig. 16. Difference in sound insulation oi 38-cm wall of hollow concrete blocks with polystyrene layer and 20-cm inner leaf. ~ ) sound reduction index R1 (38 cm wall) minus R2 (20 cm wall); (- -) vertical flanking-normalized sound level difference Dn~r (38 cm wall) minus Dn,L2 (20 cm wall).

Outer walls with external heat insulation M a n y o u t e r walls in A u s t r i a are c o v e r e d b y a heat insulation system (W~irmed~immverbundsystem) f r o m p o l y s t y r o l glued to the o u t e r surface o f the wall a n d c o v e r e d with a thin layer (-- 5 m m ) o f plaster. M e a s u r e m e n t s were c a r r i e d o u t with t w o e x a m p l e s o f 20-cm c o n c r e t e walls (295 kg/m2 a n d 340 kg/m 2) with a n d w i t h o u t 6 c m p o l y s t y r o l insulation. T h e results o f the m e a s u r e m e n t s are s h o w n in Fig. 17 for the 340-kg/m: wall. It c a n be seen t h a t the r e s o n a n c e o f the mass-spring system plaster o n p o l y s t y r o l influences the s o u n d r e d u c t i o n index. H o w e v e r , it has n o influence o n the flanking s o u n d insulation. F o r walls with o u t e r heat

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Fig. 17b. Difference in sound insulation of 20-cm wall of concrete blocks with and without layer of polystyrene. ( ~ ) Sound reduction index R i (20 cm wall + polystyrene) minus R2 (20 cm wall with plaster); (..... ) vertical flanking-normalized sound level difference Dn,L.j (20 cm wall + polystyrene) minus D.,L.2 (20 cm wall with plaster); ( - - - ) horizontal flanking-normalized sound level difference D..k~ (20 cm wall with layer of polystyrene) minus Dn.L,2 (20 cm wall with plaster).

insulation the sound insulation of the wall without this system can be inserted in the calculation of the flanking sound insulation. In Table 2 calculated and measured values are compared.

SUMMARY Test facilities have been constructed to measure flanking sound transmission in outer walls in horizontal and vertical direction with different types of junctions. Measurements of flanking-normalized sound level

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TABLE 2

Calculated and Measured Values for Flanking-Normalized Sound Level Difference Flanking outer wall

Partition

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20-cm concrete hollow blocks (295 kg/m2), polystyrol on outer surface

floor (615 kg/m 2) partition wall (250 kg/rn 2)

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20-cm concrete blocks (330 kg/m2), polystyrol on outer surface

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b Weighted sound reduction index derived from value measured on wall with plaster on both sides. difference, j u n c t i o n level difference, level difference with d i s t a n c e f r o m j u n c t i o n , r a d i a t i o n efficiency h a v e been c a r r i e d out. R e s u l t s f r o m m e a s u r e m e n t s o n different t y p e s o f o u t e r walls, w h i c h arc usual in A u s t r i a s h o w t h a t f o r m u l t i l a y e r e d b r i c k s a n d c o n c r e t e b l o c k s the f l a n k i n g s o u n d i n s u l a t i o n h a s to be m e a s u r e d a n d c a n n o t be calculated f r o m the s o u n d r e d u c t i o n index o f the wall, as is possible for h o m o g e n o u s m a s s i v e walls.

REFERENCES 1. Lang, J. Wirtschaftliche Erftillung des normgem~Ben Schallschutzes in Wohnungsbau. Fachverband der Stein- und keramischen Industrie. Wien, 1985~ 2. Sound insulation requirements and basic data for design. In Proceedings ~! the 5th F A S E S y m p o s i u m , Thessaloniki 1985. 3. O N O R M B 8115 Schallschutz und Raumakustik im Hochbau, Tell 4 MaBnahmen zur Erftillung der schalltechnischen Anforderungen, 1991. 4. O N O R M S 5101 Bauakustische Messungen--Messung von Luft- und Trittschalld~immung an Bauteilen in Priffst~inden, 1986.